Method and apparatus for sink and float separation for minerals of small particle size



March 17, 1959 N. L. DAVIS 2,877,897

METHOD AND APPARATUS FOR SINK AND FLOAT SEPARATION FOR MINERALS OF SMALL PARTICLE SIZE Filed Dec 21, 1955 2 Sheets-Sheet 1 8702 eyS March 17, 1959 DA 2,877,897

METHOD AND APPARATUS FOR SINK AND FLOAT SEPARATION FOR MINERALS OF SMALL PARTICLE SIZE Filed Dec. 21, 1955 2 Sheets-Sheet 2 IHZ/n 3 0?"- JVeZson Z-J 'V 5y J ar/ief a? garter .izzorizeys United States METHOD AND APPARATUS FOR SINK AND FLOAT SEPARATION FOR MINERALS OF SMALL PARTICLE SIZE Nelson L. Davis, Chicago, Ill.

Application December 21, 1955, Serial No. 554,586

4 Claims. (Cl. 209-1725) The present invention is directed to a method and apparatus using a dense media separating liquid to accomplish a float and sink separation of substances having unlike density characteristics. It may be used, for example, in separating coal of desired density from free impurities, slate and pyritic sulphur. In the case of coal the density of the liquid medium in the bath is established and maintained to cause the coal of desired specific gravity to float and that of undesired higher specific gravity as well as the free impurities to sink. Another example of use is metallic ore. In this case the density of the liquid medium in the bath is established and maintained so that the ore having suitably high metallic content sinks in the bath while the undesired minerals float.

A major purpose of the present invention is the provision of a method and apparatus to upgrade the small sizes of coal and other minerals by using a dense media separating liquid in a float and sink separation system. By small sizes I refer to mineral particles having a size range such as one inch ring size down to 48 mesh. In some cases, the top size limit may be larger and the bottom or lower size limit may be smaller. Float and sink separations by dense media are widely used today but experience has taught that best results are economically achieved only when the mineral particles treated are larger than /8 inch cube size and more generally when they are larger than 4 inch cube size. The present invention accomplishes a float and sink separation by dense media of much smaller particle sizes. With the present invention, for example, the particles treated may be as small as millimeter cube size.

Conventional dense media systems for separating minerals of unlike specific gravity may be classified into three groups, viz:

(1) Where the sedimentation of the media is retarded by admixtures of finely ground solids because it is desired to eliminate or minimize all hydraulic currents within the body of the bath medium with the object of improving the sharpness of the float-sink separation.

(2) Where the sedimentation is retarded and stable density conditions are attempted by introducing medium to the bath and then withdrawing it in such a manner as to result in a hydraulic current through the bath, which current is basically horizontal.

(3) Where the sedimentation of the media is prevented by introducing medium to the bottom of the bath and then withdrawing it at the surface so as to result in a rising hydraulic current having a velocity approximately equal to the settling rate of the media.

With each of these three conventional dense media systems, the treatment of minerals having a particle size smaller than A" (ring size) has generally been met by difficulties originating from the fact that the settling velocity of small size sink particles is too slow to permit an accurate float-sink separation to be made at sustained capacity rates which are commercially economical. The above difliculty is further augmented by the 2,877,897 Patented Mar. 17, 1959 fact that teeter material (that is to say solids having a density only slightly greater or slightly less than that of the bath) is characterized by exceedingly slow settling velocity. As a result it is necessary to reduce the feed rate until it is in consonance with the settling rate of the teeter solids. A further handicap has been experienced at the surface of the bath. Here a condition of congestion occurs when the float layer becomes more than one particle size in thickness. In consequence, near gravity sink or teeter does not have the mass needed to penetrate the congested surface layer in order to settle and be separated from the float solids. Here, again, the feed rate must be reduced to avoid the condition described and the result has been considered uneconomical.

One system of employing a dense medium for effecting the sink and float separation of fine coal and the like is set forth in my copending application, Serial No. 286,250 which was filed on May 6, 1952, issued on August 28, 1956, as Patent No. 2,760,633. This system utilizes the principle of retaining the media in hydraulic suspension by means of slowing rising currents induced by medium entering the lower portion of the separating bath. This principle is also set forth in my United States Patent Numbers 2,688,423, 2,521,152 and 2,516,962. The separatory vessel in this system utilizes the principle of submerging all feed material and then releasing it at a lower zone of the bath so that the float will rise to the surface due to buoyancy and thus be separated from the sink fraction of the feed material. The present invention results from tests, observations, and conclusions which were made possible through operating an actual plant in which this type of equipment or system was installed. The results proved that a float product could be gained which was practically void of misplaced sink but ditficulties were experienced in gaining a sink product which did not contain an excessive amount of misplaced float.

According to the present invention these as well as the other aforementioned difiiculties are overcome by using a separatory vessel which has a weir discharge for the floats and means for discharging the sinks from the lower portion of the vessel. The feed material is preconditioned by wetting and desliming, followed by the removal of excessive moisture and is then fed into a rotating well which retains the material en masse. Initially portions of the retained feed solids will float on the surface of the medium but as additional feed material enters the well the superimposed weight supplies the force needed to disgorge such solids from the lower open end of the feed well and at a level below that of the bath surface. The influent medium enters the bath through a circumferential orifice at a level generally intermediate the top and bottom of the bath thus generating a hydraulic current radially outward through which sink material must penetrate.

The sink solids before reaching the above described zone are agitated by a rotating structure and the currents produced thereby, which tend to break up any clusters which may contain small particles of both floats and sinks.

One portion of the influent medium having passed through the above described circumferential orifice, and having been dispersed radially outward, flows downward and is withdrawn from the bath through a discharge duct operated as a syphon or by such means as a pump or air lift. The remainder of the influent medium flows upward to be discharged over a weir. Thus all zones of the bath are activated by positive current under controlled conditions for both direction and velocity.

The zone of the bath which is immediately above that level or plane of demarcation between the upwardly rising currents and the downwardly moving currents is a restricted area as compared with the uppermost portion of the bath. That portion of the bath which is below this line or plane also has a restricted area. The velocity of flow in those portions of the bath immediately below and immediately above this plane or line is thus increased considerably. Those teeter particles which reach this line and tend to move upwardly away from this line, are quickly moved by the rising current. Those teeter particles which reach this line and tend to move downwardly are caused to descend at a relatively high velocity. Thus, teeter particles are removed effectively from that zone where they would, in conventional systems, tend to accumulate and congest the bath.

The invention also includes means for increasing and decreasing the velocity of the downwardly moving currents in accordance with individual requirements as well as means for varying the point of admission of the infiuent medium.

Referring generally now to the drawings:

Figure 1 is flow sheet illustrating the principles of the invention; and

Figure 2 is a vertical section taken on the line 2-2 of Figure 1.

In the drawings and specification like characters designate like elements throughout.

Referring specifically now to the drawings and in the first instance to Figure 1, 1 diagrammatically represents any suitable means for classifying the feed material and eliminating the small particles smaller than 48 mesh, instrumentalities for wetting the feed material, and dewatering the feed material to a general amount of surface moisture. There are many equivalent mechanisms and systems for accomplishing this end and it is not thought necessary to illustrate any particular system in detail. It is sufiicient for purposes of the present invention that the feed material in a classified and dc watered condition enters a feeding trough 2.

A separatory vessel is designated at 3 and is shown in the form of an inverted cone having a discharge weir 4 at the upper portion thereof. The vessel is adapted to contain a dense medium parting liquid, such as is formed by finely divided particles of magnetite suspended in a liquid, such as water, and maintained in suspension by circulation. An outlet pipe 5 for the sinks and medium leads from the lowermost portion of the vessel 3 to a discharge point 6. Any suitable valve 7 may be provided in the pipe 5 to regulate the flow therethrough. It should be noted that the uppermost portion of the pipe 5 is below the level of the weir 4 so that a static head will force medium out through the pipe 5 and through the discharge opening 6. After the medium and sinks pass the discharge point 6 they may be taken to any suitable facilities or system 8 for recovering the media from the sinks. The details of the system or mech anism 8 do not form part of the present invention and for this reason they are illustrated diagrammatically. The system 8 may be taken as generally representative of any system for further treatment of the medium and sink material after separation in the vessel 3.

The float material along with medium are discharged over the weir 4 into a system or mechanism 9 for further processing which will be understood by those skilled in the art. It should be understood that the bath liquid is supplied in sufiiciznt quantity to maintain the proper specific gravity of the bath as well as maintaining a sufficient body of liquid to insure discharge over the weir 4 as well as through the pipe 5. Systems for attaining these conditions are well known to those skilled in the art and the details of such systems do not in themselves form part of the present invention. They are not shown in the drawings.

The discharge weir 4 may extend for a full 360 degrees around the upper surface of the separatory vessel 3 or may extend for any smaller and practical portion thereof.

According to the present invention, the feed chute 2 has its discharge end disposed within a rotating welllik structure 10 which is generally coaxial with the axis of the vessel 3. The well-like structure has its lower end portion, designated at 11, positioned below the upper surface of the bath so that the feed material passing downwardly through the well 10 is released from the well 10 at a point well below the surface of the bath. Beams 12, 13 and 14 extend above and across the upper portion of the separatory vessel 3 and serve to support the well 10, as by the bearings 15. Any suitable motor 15a is supported by the beams 13 and 14 and serves to rotate, by means of a pinion gear 16, a ring gear affixed to the well 10. Positioned internally of the well 10 and extending downwardly therethrough is a hollow column or tube 17 which may be supported on the well 10 by any suitable ribs 18. Designated at 19 is a medium feed pipe which directs the infiuent medium downwardly through the tube 17 Thus as the preconditioned feed material is fed to the revolving well-like structure 10, it is formed into a generally hollow mass extending around the column 17 and the weight of material superimposed will force the mass downwardly below the lower edge portion 11 of the well-like structure, where it is released to float or sink in the bath depending on its density. The heaviest particles will sink towards the bottom of the vessel 3.

Positioned at the lower end of the column 17 is a cone 20, the base 22 of which is spaced inwardly from the wall of the vessel 3. Superimposed on the surface of the cone 20 is a second cone 21, the upper portion of which is joined to the lower portion of the column 17. Ribs 20a supply the connections between cones 20 and 21. The body of the cone 21 is preferably corrugated and is spaced from the wall of the cone 20 by ribs 2011 so as to provide passages for the medium therebetween. The ribs 201: may take the form of the inner portions of the cone 21 or separate members joined to the cone 20 and cone 21. Since the cone 21 is positioned beneath the well 10, particles having a density greater than that of the medium will move downwardly towards the corrugated surface presented by the cone 21. Clusters containing both high and low density particles are thus exposed to the slipstream agitation of the rotating corrugated surface of the cone 21, and such clusters are thereby disintegrated. During rotation of this surface, the corrugations will produce currents tending to agitate the clusters and break them up into small particles. Furthermore, the inclination of the surface 21 tends to direct the solids outwardly toward the wall of the vessel 3.

The medium is admitted through the pipe 19 and flows downwardly through the pipe 17 and through the space between the cone 20 and cone 21. It is discharged in the form of a radially extending curtain at a level adjacent to the base of the cone 20.

It should be noted that the effect of the cones 20 and 21 is to gradually decrease the cross-sectional area of the bath down to the base 22 of the cone. Thus the velocity of the rising currents will be greatest immediately above the base 22 and the velocity of the currents will gradually decrease as they move upwardly in the bath, due to the progressively larger cross-sectional area of the vessel.

Afiixed to the base 22 of the cone 20 is an inverted conic surface 23 integrally connected to the cone 20, which is vented at 24. The inclination of the surface 23 is such that it is generally parallel to the conic surface of the vessel 3. The effect of the surface 23 is to materially reduce the cross-sectional area of the channel beneath the base 22 of the cone 20. Thus the velocity of the currents in the channel formed between the wall of the vessel 3 and the conic surface 23, will be much greater than would be the case if cone 23 were omitted. The

velocity will increase as the current progresses downwardly to the bottom of the vessel.

Thus by the use of the rotating conic structures 20, 21 and 23, the disposal time for the rising and settling teeter particles is greatly decreased. The teeter particles which are of a density quite close to that of the bath are positively moved away from the neutral zone between the rising currents and the descending currents. Thus, any accumulation or build-up of the teeter material in the more or less neutral zone, is avoided.

I also include a means for increasing and decreasing the velocity of the downwardly moving current in the vessel. 1 illustrate in Figure 2, for example, any suitable extensible assemblies 25 and 26 which as shown, may take the form of hydraulic jacks for raising and lowering the beams 12, 13 and 14 which carry the rotating structure. Lowering the rotating structure from the position illustrated in Figure 1 further reduces the cross-sectional flow area below the base 22 and thus further increases the velocity of downward flow. Conversely, raising the rotating structure will increase the cross-sectional flow area below the base 22 and thus decrease the velocity of downward current flow. It should be noted that raising and lowering the rotating structure also has the eifect of varying the point of delivery of the medium. The exact plane or level of the base 22 for most efficient operation will vary with the characteristics of the material being separated.

In practice, when the rotating structure is in the raised position, the descending current velocity is less, and therefore less of the teeter material reports with the sink product. The converse is true when the rotating structure is in the lowered position. A range of operating adjustments between these limits is thus made available.

Whereas I have shown and described an operative form of my invention, I wish it to be understood that this showing is to be taken in an illustrative or diagrammatic sense only. There are many modifications to the invention which will fall within the scope and spirit of the invention and which will be apparent to those skilled in the art. The scope of the invention should be limited only by the scope of the hereinafter appended claims.

I claim:

1. A separatory system for heavy media sink and float separation of minerals comprising a separatory vessel in the form of an inverted cone having a discharge outlet for sink material and medium at the lower portion thereof and an overflow weir for the discharge of float material and medium, a well-like rotating structure positioned above the vessel and adapted to deliver feed material below the surface of the bath in the vessel, means for delivering feed material to said well-like structure, a hollow tube carried by said rotating structure and extending downwardly through said vessel, said tube at the lower end thereof having a generally conic surface extending outwardly toward the surface of the vessel and a second generally conic surface affixed to and beneath said first named surface while spaced therefrom for the passage of medium therebetween, means for delivering medium through said tube and through the space between said conic surfaces, and a third generally conic surface aflixed to the lower portion of said second conic surface and extending generally parallel to the wall of said vessel so as to provide a restricted flow area between said last named conic surface and the wall of said vessel.

2. The structure of claim 1 characterized by and including means for raising and lowering said rotating structure so as to thereby vary the flow area between the wall of said vessel and said conic surfaces.

3. The structure of claim 1 wherein said first named conic surface is generally corrugated whereby upon rotation of said first named surface, the bath is agitated for breaking up cluster of particles in the vicinity of said first named surface.

4. The structure of claim 1 wherein said discharge outlet includes a pipe adapted to carry sink material and medium from the vessel by virtue of a static hydraulic differential head between the upper surface of the bath and the delivery end pipe.

References Cited in the file of this patent UNITED STATES PATENTS 1,614,876 Chance Jan. 18, 1927 2,203,601 Rakowsky et al June 4, 1940 2,363,066 Ladd Nov. 21, 1944 2,552,378 McNeill May 8, 1951 2,590,756 Colin et al. Mar. 25, 1952 2,621,791 Bitzer Dec. 16. 1952 

